The present invention relates to portable working machines. More particularly, the present invention relates to a portable working machine, such as a chain saw, a blower, or a brush cutter, provided with a control unit for performing various controls using an engine temperature as a parameter.
Electronic controllers are currently employed for controlling automobile engines and motorcycle engines. Japanese Patent Laid-Open No. 2000-52280 discloses a chain saw. A portable working machine, such as a chain saw or a brush cutter, typically employs a combination of an air-cooled single cylinder engine and a carburetor. An increasing number of engines applied to this kind of working machine is controlled electronically.
Japanese Patent Laid-Open No. 2010-151125 discloses a working machine that employs an electronic controller for controlling the engine at start of the same. To be more specific, the working machine disclosed in Japanese Patent Laid-Open No. 2010-151125 is provided with a microcomputer. The microcomputer is supplied with electrical power by a power generating mechanism that starts generating electric power as the engine starts up. The microcomputer receives an engine speed signal. Then, the microcomputer performs ignition control of stopping operation of the spark plug when an engine speed immediately after the engine start-up is higher than a predetermined speed.
Japanese Patent Laid-Open No. 56-54940 proposes that a temperature sensing member be installed on a cylinder head for engine control. The temperature sensing member is constituted by a bimetal and a casing. To be specific, the cylinder head has a recess. The temperature sensing member is bolted to the cylinder head, with the bimetal inserted in the recess.
The casing accommodates the bimetal and first and second control valves. The first control valve is used for starter control. The second control valve is used for leak air control. The first and second control valves are directly driven by the bimetal. The starter control valve and the leak air control valve are related to a carburetor. When an engine temperature increases, the first control valve for starter control is shifted toward a closed position, while the second control valve for leak air control is shifted toward an open position. This changes a gas mixture to be supplied to the engine from rich to lean.
Japanese Patent Laid-Open No. 56-54940 discloses a mounting position and a mounting structure of the temperature sensing member formed by combining the two control valves associated with an air passage leading to the carburetor, and the bimetal having the two control valves fixed thereto.
As described above, most automobile engines and motorcycle engines are currently controlled electronically. Single cylinder engines for portable working machines also tend to include electronic control to improve engine performance to be more accurate. For example, electronic control of the portable working machine includes control using an engine temperature as a parameter, typically, fuel amount increasing correction control at the engine start as in Japanese Patent Laid-Open No. 56-54940.
In an air-cooled engine employed in portable working machine, an engine load is related to an engine temperature. That is, the engine temperature increases in a short time in response to an increase in the engine load. In contrast, the engine temperature decreases when there is no engine load. In order to know the engine conditions, the engine temperature is easy to detect. Accordingly, the control using the engine temperature as a parameter is employed in the electronic control of the portable working machine. Examples of the electronic control include fuel amount control in accordance with an engine load during driving.
An object of the present invention is to provide an air-cooled engine that allows a temperature sensor detecting the engine temperature to provide excellent responsivity.
Another object of the present invention is to provide an air-cooled engine that requires reduced assembling and replacement works of the temperature sensor component detecting the engine temperature.
A further object of the present invention is to provide an air-cooled engine that inhibits accidental disconnection of a wire between a temperature sensor and a control unit.